Basically, a wind turbine produces electricity in the following manner: the wind makes the rotor of the wind turbine rotate, which causes the rotation of a generator (a dynamo) producing electricity.
The main components of the nacelle of a wind turbine are:                Rotor: it is constituted of several blades collecting the wind; it is screwed to the main shaft.        Main shaft: between rotor and step-up gear.        Step-up gear: connected between the rotor (at the other end of the main shaft) and the electricity generator.        Electricity generator.        Ring system: allows rotation of the necelle in order to face the wind according to the signal of the wind vane connected to the control system.        Control system: controls the majority of the parts of the wind turbine; thus, for example, it controls the ring system.        
A wind park is made up of one or more wind turbines (up to hundreds) and other elements such as a transformation center or electric substation, and one or more meteorological towers. All these elements are normally supervised by a park supervision and control system (or remote control) installed in a central computer located in the wind park itself and connected to the wind turbines through a local communications network. The application installed in this central computer collects the operation variables of said elements, as well as the alarms produced in them.
The difficulty of applying traditional predictive maintenance techniques in wind turbines is mainly based on the following aspects:                a) the need to install a large amount of predictive equipment- one per machine-and, therefore, the generation of large amounts of information which will be necessary to process in order to detect possible problems;        b) the difficulty in accessing the data due to the location of the prediction equipment— located in the nacelle of each wind turbine and the wind turbines, in turn, in locations far from urban centers—;        c) the need to simplify maintenance and minimize the cost of each system; and,        d) the need to condition signal capturing to a specific operating condition of the wind turbine and that this operating is maintained during signal capturing for the purpose of eliminating noises introduced by transient behaviors of the wind turbine, and to obtain useful information on the condition of the critical components of the wind turbine.        